Solid electrolytic capacitor containing a protective adhesive layer

ABSTRACT

An electrolytic capacitor containing a protective adhesive layer positioned between the dielectric layer and the solid electrolyte layer (e.g., a conductive polymer layer, manganese dioxide) is generally disclosed. The protective adhesive layer can include a polymer having a repeating unit with a functional hydroxyl group, such as poly(vinyl alcohol). For instance, the polymer can be at least 90 mole % hydrolyzed. The polyvinyl alcohol can be a co-polymer of vinyl alcohol and a monomer, such as an acrylic ester like a methacrylic ester (e.g., methyl methacrylate).

BACKGROUND OF THE INVENTION

Electrolytic capacitors (e.g., tantalum capacitors) are increasinglybeing used in the design of circuits due to their volumetric efficiency,reliability, and process compatibility. For example, one type ofcapacitor that has been developed is a solid electrolytic capacitor thatincludes an anode (e.g., tantalum), a dielectric oxide film (e.g.,tantalum pentoxide, Ta₂O₅) formed on the anode, a solid electrolytelayer, and a cathode. The solid electrolyte layer may be formed from aconductive polymer, such as described in U.S. Pat. Nos. 5,457,862 toSakata, et al., 5,473,503 to Sakata et al., 5,729,428 to Sakata, et al.,and 5,812,367 to Kudoh, et al. In some electrolytic capacitors, apolymeric layer can be included between the dielectric oxide film andthe solid electrolyte layer or cathode. For example, esters ofunsaturated or saturated fatty acids have been used to form such apolymeric layer. See, e.g., U.S. Pat. No. 6,674,635 of Fife, et al. andU.S. Pat. No. 6,864,147 of Fife, et al. However, a need for animprovement nevertheless remains.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that comprises an anode; adielectric layer overlying the anode; a protective adhesive layeroverlying the dielectric layer; and a solid electrolyte layer overlyingthe protective adhesive layer. The protective adhesive layer comprises apolymer having a repeating unit with a functional hydroxyl group.

Other features and aspects of the present invention are set forth ingreater detail below.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstruction.

Generally speaking, the present invention is directed to an electrolyticcapacitor containing a protective adhesive layer positioned between thedielectric layer and the solid electrolyte layer (e.g., a conductivepolymer layer). The protective adhesive layer can improve the adherenceof the solid electrolyte layer to the dielectric layer improving thecoverage of the solid electrolyte, and thus increasing the capacitanceof the resulting electrolytic capacitor. For example, the protectiveadhesive layer can, through attraction forces (e.g., van Der Waals,ionic bonding, hydrogen bonding), bond to the dielectric layer and/orthe solid electrolyte layer to adhere the layers together. As such, thedielectric layer and/or the solid electrolyte layer can be stronglyadhered to each other.

The solid electrolytic capacitor of the present invention generallycontains an anode formed from a valve metal composition. The valve metalcomposition may have a high specific charge, such as about 5,000microFarads*Volts per gram (“μF*V/g”) or more, in some embodiments about10,000 μF*V/g or more, in some embodiments from about 15,000 μF*V/g toabout 250,000 μF*V/g or more. The valve metal composition contains avalve metal (i.e., metal that is capable of oxidation) or valvemetal-based compound, such as tantalum, niobium, aluminum, hafnium,titanium, alloys thereof, oxides thereof, nitrides thereof, and soforth. For example, the anode may be formed from a valve metal oxidehaving an atomic ratio of metal to oxygen of 1: less than 25, in someembodiments 1: less than 2.0, in some embodiments 1: less than 1.5, andin some embodiments, 1:1. Examples of such valve metal oxides mayinclude niobium oxide (e.g., NbO), tantalum oxide, etc., and aredescribed in more detail in U.S. Pat. No. 6,322,912 to Fife, which isincorporated herein in its entirety by reference thereto for allpurposes.

Conventional fabricating procedures may generally be utilized to formthe anode. In one embodiment, a tantalum or niobium oxide powder havinga certain particle size is first selected. The particle size may varydepending on the desired voltage of the resulting electrolytic capacitorelement. For example, powders with a relatively large particle size(e.g., about 10 micrometers) are often used to produce high voltagecapacitors, while powders with a relatively small particle size (e.g.,about 0.5 micrometers) are often used to produce low voltage capacitors.The particles are then optionally mixed with a binder and/or lubricantto ensure that the particles adequately adhere to each other whenpressed to form the anode. Suitable binders may include camphor, stearicand other soapy fatty acids, Carbowax (Union Carbide), Glyptal (GeneralElectric), polyvinyl alcohols, napthaline, vegetable wax, and microwaxes(purified paraffins). The binder may be dissolved and dispersed in asolvent. Exemplary solvents may include water and alcohols. Whenutilized, the percentage of binders and/or lubricants may vary fromabout 0.1% to about 8% by weight of the total mass. It should beunderstood, however, that binders and lubricants are not required in thepresent invention. Once formed, the powder is compacted using anyconventional powder press mold. For example, the press mold may be asingle station compaction press using a die and one or multiple punches.Alternatively, anvil-type compaction press molds may be used that useonly a die and single lower punch. Single station compaction press moldsare available in several basic types, such as cam, toggle/knuckle andeccentric/crank presses with varying capabilities, such as singleaction, double action, floating die, movable platen, opposed ram, screw,impact, hot pressing, coining or sizing. The powder may be compactedaround an anode wire (e.g., tantalum wire). It should be furtherappreciated that the anode wire may alternatively be attached (e.g.,welded) to the anode subsequent to pressing and/or sintering of theanode.

After compression, any binder/lubricant may be removed by heating thepellet under vacuum at a certain temperature (e.g., from about 150° C.to about 500° C.) for several minutes. Alternatively, thebinder/lubricant may also be removed by contacting the pellet with anaqueous solution, such as described in U.S. Pat. No. 6,197,252 toBishop, et al., which is incorporated herein in its entirety byreference thereto for all purposes. Thereafter, the pellet is sinteredto form a porous, integral mass. For example, in one embodiment, thepellet may be sintered at a temperature of from about 1200° C. to about2000° C., and in some embodiments, from about 1500° C. to about 1800° C.under vacuum. Upon sintering, the pellet shrinks due to the growth ofbonds between the particles. In addition to the techniques describedabove, any other technique for forming the anode may also be utilized inaccordance with the present invention, such as described in U.S. Pat.Nos. 4,085,435 to Galvagni; 4,945,452 to Sturmer, et al.; 5,198,968 toGalvagni; 5,357,399 to Salisbury; 5,394,295 to Galvagni, et al.;5,495,386 to Kulkarni; and 6,322,912 to Fife, which are incorporatedherein in their entirety by reference thereto for all purposes.

Regardless of the particular manner in which it is form, the thicknessof the anode may be selected to improve the electrical performance ofthe electrolytic capacitor element. For example, the thickness of theanode (in the −z direction in FIG. 1) may be about 4 millimeters orless, in some embodiments, from about 0.2 to about 3 millimeters, and insome embodiments, from about 0.4 to about 2 millimeters. Such arelatively small anode thickness (i.e., “low profile”) helps dissipateheat generated by the high specific charge powder and also provide ashorter transmission path to minimize ESR and inductance. The shape ofthe anode may also be selected to improve the electrical properties ofthe resulting capacitor. For example, the anode may have a shape that iscurved, sinusoidal, rectangular, U-shaped, V-shaped, etc. The anode mayalso have a “fluted” shape in that it contains one or more furrows,grooves, depressions, or indentations to increase the surface to volumeratio to minimize ESR and extend the frequency response of thecapacitance. Such “fluted” anodes are described, for instance, in U.S.Pat. Nos. 6,191,936 to Webber, et al.; 5,949,639 to Maeda, et al.; and3,345,545 to Bourgault et al., as well as U.S. Patent ApplicationPublication No. 2005/0270725 to Hahn, et al., all of which areincorporated herein in their entirety by reference thereto for allpurposes.

The anode may be anodized so that a dielectric layer is formed over andwithin the porous anode. Anodization is an electrical chemical processby which the anode metal is oxidized to form a material having arelatively high dielectric constant. For example, a tantalum anode maybe anodized to form tantalum pentoxide (Ta₂O₅), which has a dielectricconstant “k” of about 27. The anode may be dipped into a weak acidsolution (e.g., phosphoric acid) at an elevated temperature (e.g., about60° C.) that is supplied with a controlled amount of voltage and currentto form a tantalum pentoxide coating having a certain thickness. Thepower supply is initially kept at a constant current until the requiredformation voltage is reached. Thereafter, the power supply is kept at aconstant voltage to ensure that the desired dielectric quality is formedover the surface of the tantalum pellet. The anodization voltagetypically ranges from about 5 to about 200 volts, and in someembodiments, from about 20 to about 100 volts. In addition to beingformed on the surface of the anode, a portion of the dielectric oxidefilm will also typically form on the surfaces of the pores. It should beunderstood that the dielectric layer may be formed from other types ofmaterials and using different techniques.

According to the present invention, a protective adhesive layer isformed over the dielectric layer to help adhere the dielectric layer tothe cathode layers. The protective adhesive layer can improve theadherence of the solid electrolyte layer to the dielectric layer andincrease the capacitance of the resulting electrolytic capacitor. Forexample, the protective adhesive layer can, through attraction forces(e.g., van Der Waals, ionic bonding, hydrogen bonding), bond to thedielectric layer and/or the solid electrolyte layer to adhere the layerstogether. As such, the dielectric layer and/or the solid electrolytelayer can be strongly adhered to each other.

The protective adhesive layer can generally include a variety ofmaterials that are capable of forming a thin coating and that canimprove the electrical performance of the resulting capacitor. In oneparticular embodiment, the protective adhesive layer may include, forinstance, a polymer containing a repeating unit with a functionalhydroxyl group. As such, the resulting polymer may have at least twohydroxyl groups along the polymer chain. Suitable polymers having arepeating unit with a functional hydroxyl group include polyvinylalcohol (“PVA”), copolymers of polyvinyl alcohol (e.g., ethylene vinylalcohol copolymers, methyl methacrylate vinyl alcohol copolymers, etc.),polysaccharides, etc. The presence of hydroxyl groups in the polymer mayprovide adhesive characteristics to the protective adhesive layer thathelp bond to the dielectric layer to the solid electrolyte, such as aconductive polymer. For example, without wishing to be bound by theory,it is believed that the hydroxyl groups can increase the adhesion of thelayers through attraction and/or bonds (e.g., van Der Waals forces,hydrogen bonding, ionic bonds, covalent bonds, etc.).

Suitable vinyl alcohol polymers, for instance, have at least two or morevinyl alcohol units in the molecule and may be a homopolymer of vinylalcohol, or a copolymer containing other monomer units. Vinyl alcoholhomopolymers may be obtained by hydrolysis of a vinyl ester polymer,such as vinyl formate, vinyl acetate, vinyl propionate, etc. Vinylalcohol copolymers may be obtained by hydrolysis of a copolymer of avinyl ester with an olefin having 2 to 30 carbon atoms, such asethylene, propylene, 1-butene, etc.; an unsaturated carboxylic acidhaving 3 to 30 carbon atoms, such as acrylic acid, methacrylic acid,crotonic acid, maleic acid, fumaric acid, etc., or an ester, salt,anhydride or amide thereof; an unsaturated nitrile having 3 to 30 carbonatoms, such as acrylonitrile, methacrylonitrile, etc.; a vinyl etherhaving 3 to 30 carbon atoms, such as methyl vinyl ether, ethyl vinylether, etc.; and so forth.

The use of vinyl alcohol copolymers may be particularly desired in thepresent invention to increase the adhesion properties of the protectiveadhesive layer to the dielectric layer and solid electrolyte. An acrylicor methacrylic ester, for instance, may be copolymerized with a vinylester to provide a hydrophilic polymer having excellent adhesionproperties, while adding soft and flexible properties to the layer.Suitable esters of acrylic acid or methacrylic acid may include estersof unbranched or branched alcohols having from 1 to 15 carbon atoms.Preferred methacrylic esters or acrylic esters are methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, propylacrylate, propyl methacrylate, n-, iso- and t-butyl acrylate, n-, iso-and t-butyl methacrylate, 2-ethylhexyl acrylate, etc. The fraction ofthese comonomers may range from about 30 mol % to about 70 mole %, andin some embodiments, from about 40 mol % to about 60 mol % of the vinylalcohol copolymer.

Regardless of the monomers employed, the degree of hydrolysis may beselected to increase the adhesive properties of the polymer. Forexample, the degree of hydrolysis may be about 90 mole % or greater, insome embodiments about 95 mole % or greater, and in some embodiments,about 98 mole % or more. For a vinyl alcohol homopolymer, this wouldmean that about 90 mole % or greater, in some embodiments about 95 mole% or greater, and in some embodiments, about 98 mole % or more of theacetate groups on the parent polymer are hydrolyzed. Examples ofsuitable highly hydrolyzed polyvinyl alcohol polymers are availableunder the trade name Mowiol® from Kuraray Specialties Europe GmbH,Frankfurt, such as Mowiol® 3-98, Mowiol® 4-98, and Mowiol® 6-98.

In addition, other materials may be employed to improve the adhesivenature of the protective adhesive layer. Examples of such materialsinclude acrylate or methacrylate polymers, such as polymethylmethacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutylmethacrylate, hydroxyethylmethacrylate, etc.; polyurethane; polystyrene;esters of unsaturated or saturated fatty acids (e.g., glycerides); etc.For instance, suitable esters of fatty acids include, but are notlimited to, esters of lauric acid, myristic acid, palmitic acid, stearicacid, eleostearic acid, oleic acid, linoleic acid, linolenic acid,aleuritic acid, shellolic acid, and so forth. These esters of fattyacids have been found particularly useful when used in relativelycomplex combinations to form a “drying oil”, which allows the resultingfilm to rapidly polymerize into a stable layer. Such drying oils mayinclude mono-, di-, and/or tri-glycerides, which have a glycerolbackbone with one, two, and three, respectively, fatty acyl residuesthat are esterified. For instance, some suitable drying oils that may beused include, but are not limited to, olive oil, linseed oil, castoroil, tung oil, soybean oil, and shellac. These and other resinousmaterials are described in more detail in U.S. Pat. No. 6,674,635 ofFife et al. and U.S. Pat. No. 6,864,147 of Fife et al., both of whichare incorporated herein in their entirety by reference thereto for allpurposes.

The material(s) of the protective adhesive layer are typically moreresistive than the conductive polymer that of the solid electrolyte. Forexample, the protective adhesive layer may contain a material having aresistivity of greater than about 0.05 ohm-cm, in some embodimentsgreater than about 5, in some embodiments greater than about 1,000ohm-cm, in some embodiments greater than about 1×10⁵ ohm-cm, and in someembodiments, greater than about 1×10¹⁰ ohm-cm. Despite possessing suchinsulative properties the protective adhesive layer does not typicallyhave a significant adverse effect on the electrical performance of thecapacitor. One reason for this is due to the relatively small thicknessof the barrier, which is normally about 100 micrometers or less, in someembodiments about 50 micrometers or less, and in some embodiments, about10 micrometers or less.

The protective adhesive layer can be applied in a variety of differentways. For example, in one embodiment, the anode part or slug can bedipped into a dipping solution of the desired protective adhesive layermaterial(s). The solution may be formed by dissolving or dispersing thematerials in a solvent. The solvent is also useful in controlling theviscosity of the solution, thereby facilitating the formation of thinlayers. Any solvent of a variety of solvents may be employed, such aswater; glycols (e.g., propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, anddipropyleneglycol); glycol ethers (e.g., methyl glycol ether, ethylglycol ether, and isopropyl glycol ether); ethers (e.g., diethyl etherand tetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones; esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth.

In one particular embodiment, the polymer having a repeating unit with afunctional hydroxyl group can be water-soluble. As such, aqueoussolvents (e.g., water) may be employed due to the hydrophilic nature ofthe protective adhesive layer polymers, which can result in simplifiedprocessing and decreased costs. In fact, water may constitute about 20wt. % or more, in some embodiments, about 50 wt. % or more, and in someembodiments, about 75 wt. % to 100 wt. % of the solvent(s) used in thesolution.

Once formed, the anode part can be dipped into the dipping solution oneor more times, depending on the desired thickness of the protectiveadhesive layer. The number of layers that form the protective adhesivelayer can be from about 2 to about 10 layers, and in some embodiments,from about 3 to about 7 layers. Besides dipping, it should also beunderstood that other conventional application methods, such assputtering, screen printing, electrophoretic coating, electron beamdeposition, vacuum deposition, spraying, and so forth, can also be usedto deposit the protective adhesive layer. After forming the protectiveadhesive layer, it is often desired that the anode part be dried tofacilitate evaporation of any solvent used during application.Typically, each layer is dried at a temperature ranging from about 30°C. to about 300° C., and in some embodiments, from about 50° C. to about150° C., for a time period ranging from about 1 minute to about 60minutes, and in some embodiments, from about 15 minutes to about 30minutes. It should also be understood that heating need not be utilizedafter application of each layer, but may instead be utilized only afterformation of the entire protective adhesive layer.

Once the protective adhesive layer is formed on the dielectric layer, asolid electrolyte is formed thereon. The solid electrolyte layer can beformed of any suitable material, such as manganese dioxide (MnO₂) or aconductive polymer layer. The use of manganese dioxide in a solidelectrolyte layer is well known in the art.

In one particular embodiment, the solid electrolyte layer includes oneor more conductive polymers. Suitable conductive polymers include, butare not limited to, polypyrroles; polythiophenes, such aspoly(3,4-ethylenedioxy thiophene) (PEDT); polyanilines; polyacetylenes;poly-p-phenylenes; and derivatives thereof. If desired, the solidelectrolyte can be formed from multiple conductive polymer layers, suchas one layer formed from PEDT and another layer formed from apolypyrrole. Any suitable monomer(s) may be employed to form theconductive polymer. For example, 3,4-ethylene dioxythiophene (BAYTRON M,Bayer Corp.) may be used as a monomer for forming PEDT. An oxidativepolymerization catalyst may be employed to initiate the polymerizationof the monomer(s). The oxidative polymerization catalyst can be anytransitional metal salt useful as an oxidizing agent, such as thosetransitional metal salts derivatized with organic ligands. A preferredoxidative polymerization catalyst can be an organic acid ligand combinedwith iron (III), such as iron (III) tosylate. One suitable oxidativepolymerization catalyst is BAYTRON C, which is iron (III)toluene-sulphonate and n-butanol and sold by Bayer Corporation.

The monomer(s) (e.g., 3,4-ethylenedioxy thiophene) used to form theconductive polymer(s) (e.g., PEDT) may be mixed with an oxidativepolymerization catalyst to form the conductive polymer layer. Forexample, the monomer solution and the oxidative polymerization catalystcan be sequentially added in separate solutions, and then polymerized onthe electrolyte capacitor to form the conductive polymer.

Alternatively, the monomer(s) (e.g., 3,4-ethylenedioxy thiophene) usedto form the conductive polymer(s) (e.g., PEDT) may be mixed with anoxidative polymerization catalyst to form a polymerization solution(e.g., dispersion, emulsion, suspension, mixture, and so forth) toenhance the efficiency of the solid electrolyte forming step. Theoxidative polymerization catalyst can be present in the polymerizationsolution in any amount sufficient to cause oxidative polymerization ofthe monomer(s).

However, in one particular embodiment, less than the normally requiredmolar equivalent of the oxidative polymerization catalyst can be usedper mole of monomer in forming the conductive polymer layer (i.e., lessthan a stoichiometric amount of the oxidative polymerization catalyst).For instance, when the monomer includes 3,4-ethylenedioxy thiophene, thenormally required molar ratio used to polymerize 3,4-ethylenedioxythiophene into PEDT is about 1 mole 3,4-ethylenedioxy thiophene to about18 moles oxidative polymerization catalyst. However, the presentinventor has found that the use of less than the 18 moles of oxidativepolymerization catalyst per mole of monomer can slow the polymerizationof the monomer, creating oligomers that are shorter in length than iffully polymerized into a polymer. Without wishing to be bound by theory,it is believed that the excess monomer etches oligomers which providebetter penetration into the porous anode. Thus, less than 18 moles ofoxidative polymerization catalyst can be present in the polymerizationsolution per mole of monomer (e.g., 3,4-ethylenedioxy thiophene), suchas less than about 15 moles of oxidative polymerization catalyst permole of monomer. For example, about 5 to about 12 moles of oxidativepolymerization catalyst can be present in the polymerization solutionper mole of monomer, such as about 10 moles of oxidative polymerizationcatalyst per mole of monomer.

When mixed together in a single solution, a small portion of themonomer(s) tends to polymerize, even absent the application of heat.However, such premature polymerization may be substantially inhibitedthrough the appropriate selection of a polar solvent that functions as areaction inhibitor. In one particular embodiment, an aprotic polarsolvent capable of donating electrons can be included in thepolymerization solution. Without wishing to be bound by theory, it isbelieved that the localized negative charge on a polar solvent canattract, through electron donation (e.g., acid-base reactions), thepositively charged metal (e.g., iron III) of the oxidativepolymerization catalyst to form a weakly bonded complex. This weakcomplex may effectively inhibit the ability of the oxidativepolymerization catalyst to oxidize the monomer for polymerization. Assuch, only a relatively small amount, if any, of the monomer isprematurely polymerized in the polymerization solution prior to itsapplication to the electrolyte capacitor. Additionally, the life span onthe polymerization solution can be greatly extended.

Additionally, polar solvents, such as aprotic solvents, can act as adissolve any oligomers prematurely formed while still in thepolymerization solution. Thus, the oligomers can be inhibited fromfurther polymerization, and the shelf life of the polymerizationsolution can be extended, even if oligomers are prematurely formed. Assuch, the combination of the polar solvent and the monomer with lessthan a stoichiometric amount of the oxidative polymerization catalystcan provide further advantages to the method of producing the conductivepolymer layer.

Particularly suitable polar solvents are aprotic solvents, such asdipolar aprotic solvents, which lack an acidic proton. Polar aproticsolvents include, but are not limited to, N-methylpyrrolidone, dimethylsulfoxide, dimethylformamide, hexamethylphosphorotriamide, dimethylacetamide, methyl ethyl ketone, and so forth.

In most embodiments, the polar solvent(s) are combined with one or moreco-solvents to form a solvent system for the solution. In suchembodiments, the weight ratio of the co-solvents(s) to the polarsolvent(s) may be about 50:1 or more, in some embodiments from about50:1 to about 250:1, and in some embodiments, from about 75:1 to about150:1. For example, the polar solvent(s) may constitute from about 0.001wt. % to about 10 wt. %, in some embodiments, from about 0.01 wt. % toabout 5 wt. %, and in some embodiments, from about 0.05 wt. % to about 1wt. % of the polymerization solution. Likewise, the co-solvent(s) mayconstitute from about 20 wt. % to about 90 wt. %, in some embodiments,from about 30 wt. % to about 80 wt. %, and in some embodiments, fromabout 40 wt. % to about 60 wt. % of the polymerization solution. It isbelieved that such a small amount of polar solvent in the completesolvent system of the polymerization solution can sufficiently inhibitpremature polymerization, while still allowing polymerization onceapplied to the anode.

Any suitable co-solvent that is miscible with the polar solvent may beemployed in the present invention. Exemplary co-solvents may includeglycols (e.g., propylene glycol, butylene glycol, triethylene glycol,hexylene glycol, polyethylene glycols, ethoxydiglycol, anddipropyleneglycol); glycol ethers (e.g., methyl glycol ether, ethylglycol ether, and isopropyl glycol ether); ethers (e.g., diethyl etherand tetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; esters (e.g., ethyl acetate,butyl acetate, diethylene glycol ether acetate, and methoxypropylacetate); amides (e.g., dimethylformamide, dimethylacetamide,dimethylcaprylic/capric fatty acid amide and N-alkylpyrrolidones);nitriles (e.g., acetonitrile, propionitrile, butyronitrile andbenzonitrile); sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO)and sulfolane); and so forth. Particularly suitable co-solvent(s) arealiphatic alcohols, such as ethanol, propanol, methanol, isopropanol,butanol, and so forth.

The polymerization solution may also contain a dopant. The dopant may bean oxidizing or reducing agent, and can provide excess charge to theconductive polymer. For example, in one embodiment, the dopant can beany conventional anion. Particularly, the ions of aromatic sulfonicacids, aromatic polysulfonic acids, organic sulfonic acids including ahydroxy group, organic sulfonic acids including a carboxyl group,alycyclic sulfonic acids, benzoquinone sulfonic acids and other organicsulfonic acids can effectively stabilize the conductivity of aconducting polymer layer because their molecule sizes are large enoughto obstruct easy dedoping in a high temperature atmosphere. Examples ofsuch organic sulfonic acids are dodecylbenzene sulfonic acid, toluenesulfonic acid, benzyl sulfonic acid, naphthalene sulfonic acid, phenolsulfonic acid, sulfoisofuthalic acid, sulfosalicylic acid, camphorsulfonic acid, and adamantane sulfonic acid. In one embodiment, thedopant can be supplied from the same compound as the oxidativepolymerization catalyst. For instance, iron III toluene-sulphonate cansupply both the dopant (anion of toluene-sulphonate) and the oxidativepolymerization catalyst (cation of iron III).

A binder may also be employed in the polymerization solution tofacilitate adherence of the solid electrolyte to the dielectric layer.For example, the polymerization solution may contain organic binderswhich are soluble in organic solvents, such as poly(vinyl acetate),polycarbonate, poly(vinyl butyrate), polyacrylates, polymethacrylates,polystyrene, polyacrylonitrile, poly(vinyl chloride), polybutadiene,polyisoprene, polyethers, polyesters, silicones, and pyrrole/acrylate,vinyl acetate/acrylate and ethylene/vinyl acetate copolymers each ofwhich are soluble in organic solvents. It is also possible to usewater-soluble binders such as polyvinyl alcohols as thickeners.Alternatively, those resinous material disclosed above in relation tothe protective adhesive layers can be included in the polymerizationsolution as an organic binder.

Once the polymerization solution is formed, it may be applied to theanode part using any known technique. For instance, conventionaltechniques such as sputtering, screen-printing, dipping, electrophoreticcoating, electron beam deposition, spraying, and vacuum deposition, canbe used to form the conductive polymer coating. Although various methodshave been described above, it should be understood that any other methodfor applying the conductive coating(s) to the anode part can also beutilized in the present invention. For example, other methods forapplying such conductive polymer coating(s) may be described in U.S.Pat. Nos. 5,457,862 to Sakata, et al., 5,473,503 to Sakata, et al.,5,729,428 to Sakata, et al., and 5,812,367 to Kudoh, et al., which areincorporated herein in their entirety by reference thereto for allpurposes. Regardless of the application technique employed, thepolymerization solution may be cooled to further stabilize thepolymerization solution and prevent premature polymerization of themonomer(s). For example, the polymerization solution can be applied at atemperature of less than about 20° C., in some embodiments less thanabout 15° C., in some embodiments less than about 10° C., and in someembodiments, less than about 5° C.

Once applied, the conductive polymer may be healed. Healing may occurafter each application of a conductive polymer layer or may occur afterthe application of the entire conductive polymer coating. In someembodiments, the conductive polymer can be healed by dipping the sluginto an electrolyte solution, and thereafter applying a constant voltageto the solution until the current is reduced to a preselected level. Ifdesired, such healing can be accomplished in multiple steps. Forexample, an electrolyte solution can be a dilute solution of themonomer, the catalyst, and dopant in an alcohol solvent (e.g., ethanol).

After application of some or all of the layers described above, the slugmay then be washed if desired to remove various byproducts, excesscatalysts, and so forth. Further, in some instances, drying may beutilized after some or all of the dipping operations described above.For example, drying may be desired after applying the catalyst and/orafter washing the slug in order to open the pores of the slug so that itcan receive a liquid during subsequent dipping steps.

Once the solid electrolyte is formed, the part may then be applied witha carbon coating (e.g., graphite) and silver coating, respectively. Thesilver coating may, for instance, act as a solderable conductor, contactlayer, and/or charge collector for the capacitor and the carbon coatingmay limit contact of the silver coating with the solid electrolyte. Leadelectrodes may then be provided as is well known in the art. Typically,the silver coating includes silver and an organic binder, such as aresin (e.g., an epoxy resin).

Optionally, the formed capacitor can be coated with a barrier layer tohelp protect the capacitor from changes in its working environment. Forinstance, the barrier layer can enable the electrolytic capacitor toincrease it performance in relatively high humidity and/or hightemperature environments. The barrier layer can be positioned betweenthe graphite coating and the silver coating. Alternatively, the barrierlayer can be preferably positioned on the external surface of the silvercoating to form the outermost layer of the resulting capacitor.

The barrier layer can include a barrier polymer configured to reduceoxygen and moisture permeability of the electrolyte capacitor withoutsubstantially affecting the functionality of the coated capacitor. Forexample, the barrier polymer can block passage of oxygen and/or moisturethrough the barrier layer by forming a structure that presents atortuous path for water and/or oxygen molecules to travel. Thus, thebarrier polymer can slow the transmission of the water and/or oxygenmolecules through the barrier layer.

Additionally, the barrier polymer can adhere the barrier layer to thecapacitor, such as to the silver coating having an organic binder. Assuch, the barrier layer can be intimately applied to the capacitorwithout substantially affecting the capacitor's performance. Forexample, the barrier polymer can bond (e.g., ionic bonding, hydrogenbonding, van Der Walls attraction, etc.) to the organic binder of thesilver coating to secure the barrier layer to the capacitor. In someembodiments, these bonds can be initiated from functional hydroxylgroups positioned on the barrier polymer. The functional hydroxyl groupscan, for instance, be provided from at least two hydroxyl groups (e.g.,a polyol) or at least two alkoxy groups.

In one particular embodiment, the barrier polymer can be a polyurethanehaving multiple hydroxyl groups (e.g., a polyurethane diol). Forexample, the polyurethane can be selected from the family of polyetherpolyols, which have multiple hydroxyl groups capable of bonding to theorganic binder of the silver coating. Additionally, polyurethanepolymers generally have good barrier properties, and are generallystable in high temperature and/or high humidity environments. Analternative group of barrier polymers can be polyesters havingfunctional alkoxy groups capable of bonding to the organic binder of thesilver coating, similar to the functional hydroxyl groups discussedabove.

In some embodiments, the barrier and adhesive properties of the barrierpolymer can be increased by crosslinking the barrier polymer to form a3-dimensional crosslinked network. For instance, the barrier polymer canbe crosslinked by combining a polyfunctional crosslinking agent with thebarrier polymer to produce the barrier layer. The addition of apolyfunctional crosslinking agent can provide improvements in adhesion,heat resistance, water and moisture resistance, and oxygen resistance tothe barrier layer.

For example, the polyfunctional crosslinking agent can be anitrogen-containing polymer. For example, a polymer containingpolyfunctional aziridine groups can be utilized as a polyfunctionalcrosslinking agent. The term “aziridine” as used herein refers to analkyleneimine group, and “polyfunctional aziridine” includes compoundsproduced by the polymerization of an alkyleneimine, such asethyleneimine, ethylethyleneimine, propyleneimine, and mixtures andderivatives thereof. As such, the polyfunctional aziridine can includepolyalkyleneimine polymers (e.g., polyethyleneimine,polyethylethyleneimine, and polypropyleneimine) or copolymers, and theirderivatives. In one particular embodiment, the polyfunctionalcrosslinking agent can include polyethylenenimine, such as branchedpolyethyleneimine.

Without wishing to be bound by theory, it is believed thatpolyfunctional crosslinking agent can promote adhesion of the barrierlayer to the capacitor by crosslinking the barrier polymer of thebarrier layer with itself and to the organic binder of the silvercoating. Also, the crosslinked barrier polymer can have increasedbarrier properties due to its crosslinked chemical structure thatprovides a more tortuous path through the barrier layer for the water oroxygen molecules. Also, crosslinking the barrier polymer provides thebarrier layer with increased mechanical strength due to the crosslinkedchemical structure of the barrier polymer and/or the polyfunctionalcrosslinking agent.

In one embodiment, polyalkyleneimine polymers (e.g., polyethyleneimine)are preferred due to their ability to form crosslinked structuresthemselves, in addition to crosslinking the polyurethane. For example,branched polyethyleneimine generally contains primary, secondary, andtertiary amines. These amine groups can provide bonding sites formingintermolecular bonds (e.g., hydrogen bonds, van Der Waals bonds, and/orionic bonds) with other amine groups, with functional groups of thepolyurethane, and possibly with any functional groups located on thesurface of the capacitor. For example, when the barrier layer is appliedto a silver or graphite coating containing an organic binder, thepolyfunctional crosslinking agent can chemically attract, or possiblyeven bond, polymers of the barrier layer to the organic binder of thesilver and/or graphite coatings. Additionally, polyalkyleneiminepolymers are relatively polar polymers, allowing them to reduce thesurface tension of any applied liquid (e.g., water vapor) to the barrierlayer.

Another nitrogen-containing polymer useful as a polyfunctionalcrosslinking agent includes polyamides and derivatives and copolymersthereof. For instance, one particular polyamide useful as apolyfunctional crosslinking agent can be a polyamideimide. Otherpolyfunctional crosslinking agents can include polyfunctional isocyanatecompounds having at least two or more isocyanate groups. Representativeorganic diisocyanates suitable for the primer coating are aromaticdiisocyanates such as 2,4 tolylene diisocyanate,methylene-bis-p,p′-phenylene diisocyanate, 1,5-naphthalene diisocyanate,polymethylene diisocyanate such as tetramethylene diisocyanate,pentamethylene diisocyanate, hexamethylene diisocyanate, decamethylenediisocyanate, cycloalkylene diisocyanate such as cyclohexylene1,4-diisocyanate, diisocyanates containing heteroatoms in the chain, andmixed isocyanates-isothiocyanates such as 1-isocyanate,6-isothiocyanatehexane. Other examples include toluenediisocyanate (TDI),triphenylmethanetriisocyanate (TTT), isophoronediisocyanate (IPDI),tetramethylxylenediisocyanate (TMXDI) or polymers or derivativesthereof.

If desired, the barrier layer may include other auxiliary substanceswhich may be added to the final composition in relative amounts in orderto impart desirable properties or to suppress undesirable properties.Examples of such substances include viscosity modifiers, dispersant,fillers, plasticizers, pigments, dyes, wetting agents, heat stabilizers,carbon black, silica sols, leveling agents, antifoaming agents,UV-stabilizers and the like. The composition may also be blended withother polymer dispersions such as polyvinyl acetate, epoxy resins,polyethylene, polybutadiene, polyvinyl chloride, polyacrylate and otherhomopolymer and copolymer dispersions.

Of course, the barrier layer is not limited to those materials describedabove. For example, the barrier layer may include any suitable materialuseful for inhibiting the passage of oxygen and/or water through thelayer. For instance, any resinous material (e.g., epoxy) can be utilizedto form a barrier layer.

Since permeability is a function of diffusion, a thicker coat weightslows permeability. Thus, varying the film thickness affects the oxygenand moisture vapor transmission rate. However, the advantage of athicker barrier layer must be weighed against any adverse affect that athicker coat may impart on the performance of the resulting coatedcapacitor.

Thus, as a result of the present invention, a capacitor may be formedthat exhibits excellent electrical properties. For instance, it isbelieved that the protective adhesive layer of the present inventionimproves the mechanical stability of the interface between theconductive polymer and the dielectric layer. This mechanically stableinterface can result in a highly continuous and dense conductive polymerwith high conductivity, thereby providing low equivalent seriesresistance (ESR). The equivalent series resistance of a capacitorgenerally refers to the extent that the capacitor acts like a resistorwhen charging and discharging in an electronic circuit and is usuallyexpressed as a resistance in series with the capacitor. For example, acapacitor of the present invention typically has an ESR less than about1000 milliohms (mohms), in some embodiments less than about 500 mohms,and in some embodiments, less than about 100 mohms.

Additionally, when a capacitor is formed having a barrier layer asdescribed above, the resulting capacitor can have an ESR less than about1000 milliohms (mohms), in some embodiments less than about 500 mohms,and in some embodiments, less than about 125 mohms, even after aging for1000 hours at 85° C. and at 85% relative humidity. Thus, a capacitorformed having a barrier layer as described above can have a relativelysmall change in ESR after aging for 1000 hours at 85° C. and at 85%relative humidity (when compared to its ESR before aging), such as lessthan 500%, in some embodiments, less than 100%, and in some embodimentsless than 25%.

In addition, after the anode is healed through the application ofvoltage, the resulting leakage current, which generally refers to thecurrent flowing from one conductor to an adjacent conductor through aninsulator, can be maintained at relatively low levels due to themechanical stability of the interface provided by the protectiveadhesive layer. For example, the numerical value of the normalizedleakage current of a capacitor of the present invention is, in someembodiments, less than about 0.1 μA/μF*V, in some embodiments less thanabout 0.01 μA/μF*V, and in some embodiments, less than about 0.001μA/μF*V, where μA is microamps and μF*V is the product of thecapacitance and the rated voltage.

The present invention may be better understood by reference to thefollowing examples.

TEST PROCEDURES

Equivalent Series Resistance (ESR), Capacitance, and Dissipation Factor:

Equivalence series resistance and impedance were measured using aKeithley 3330 Precision LCZ meter with Kelvin Leads with 0 volts biasand 1 volt signal. The operating frequency was 100 kHz. The capacitanceand dissipation factor were measured using a Keithley 3330 Precision LCZmeter with Kelvin Leads with 2 volts bias and 1 volt signal. Theoperating frequency was 120 Hz and the temperature was 23° C.±2° C.

Leakage Current:

Leakage current (“DCL”) was measured using a MC 190 Leakage test setmade by Mantracourt Electronics LTD, UK. The MC 190 test measuresleakage current at a temperature of 25° C. and at a certain ratedvoltage after 10 seconds.

EXAMPLE 1

The ability to form a tantalum capacitor having a conductive polymerlayer formed from a polymerization solution was demonstrated. Inparticular, 50,000 μFV/g tantalum powder was pressed into pellets andsintered to form a porous electrode body. The pellets were anodized in aphosphoric acid electrolyte in water and subsequently shell formed inwater/ethylene glycol electrolyte to form the dielectric layer. Aprotective adhesive layer was applied to the porous electrode body froma solution of one part by weight polyvinylalcohol and one part by weightmethyl methacrylate in ninety-eight parts of water. The solution wasformed by gently heating to 70° C. The anode pellets were immersed inthis solution and dried for 15 minutes at a temperature of 100° C.

A polymerization solution was prepared to form the conductive polymercoating. The polymerization solution prepared with twelve parts byweight ethanol, 0.3 parts per weight methyl methacrylate, 0.1 part byweight methylpyrrolidone, 1 part by weight 3,4-ethylenedioxythiophene(sold under the name Baytron® M by Bayer Corp.), and 10 parts by weightiron III tosylate in butanol (sold under the name Baytron® CB40 by BayerCorp.). The solution was used to impregnate and coat the anode pelletshaving the dielectric layer and the protective adhesive layer. The anodepellets were immersed in the polymerization solution cooled to 5° C. andkept under dry air. The monomers of the polymerization solution werepolymerized for one hour at ambient temperature and 60% relativehumidity. The anode pellets were immersed in the polymerization solutionand polymerized a total of six times to form the conductive polymerlayer.

Another polymerization solution was prepared with the same ingredientsas above in the first step, except it was diluted six times by weightethanol. The anode pellets having the conductive polymer layer wereimmersed in this solution while at 5° C. and kept under dry air andre-anodized. After re-anodization, the resulting pellets werepolymerized at ambient temperature and 60% relative humidity.

The pellets were then coated with a graphite and silver coating.

Finally, a solution comprising two parts by weight polyurethane diol(Sigma-Aldrich Co.) and two parts polyethyleneimine (Sigma-Aldrich Co.)in ninety six parts of ethanol was produced. The pellets with suchcovered cathode were immersed in this solution and then dried at 25° C.for 30 min.

The finished parts were completed by conventional assembly technologyand measured.

EXAMPLE 2

50,000 μFV/g tantalum powder was pressed into pellets and sintered toform a porous electrode body. The pellets were anodized in a phosphoricacid electrolyte in water and subsequently shell formed inwater/ethylene glycol electrolyte. The porous electrode body was appliedwith a solution one part by weight 3,4-ethylenedioxythiophene (Baytron®M, H. C. Starck GmbH), twenty parts by weight iron(III) tosylate inbutanol (Baytron® CB40, H. C. Starck GmbH) and twelve parts by weightethanol. The solution was used to impregnate of anode pellets withpre-coated dielectrics. The anode pellets were immersed in thissolution, cooled at 5° C. and kept under dry air, and then polymerizedfor one hour at ambient temperature and 60% relative humidity. The anodepellets were immersed in the polymerization solution and polymerized atotal of six times to form the conductive polymer layer.

Another polymerization solution was prepared with the same ingredientsas above in the first step, except it was diluted six times by weightethanol. The anode pellets with polymeric layer were immersed in thissolution, cooled at 5° C. and kept under dry air, and re-anodized. Afterre-anodization these pellets were polymerized at ambient temperature and60% relative humidity. The pellets were then coated with a graphite andsilver coating. The finished parts were completed by conventionalassembly technology and measured.

The parameters of the samples made are shown in Table 1:

TABLE 1 Leakage Cap DF ESR Current Capacitor (μF) (%) (mΩ) (μA) Example1 9.9 2.0 95 1.2 Example 2 9.8 1.9 122 2.0

The stability of the resulting capacitors were also tested afterexposure to different environments. Specifically, samples from eachExample 1 and the Comparative Example were exposed to an environment of85% relative humidity at 85° C. for 1000 (as shown in Table 2), andchanges in the capacitor's performance were measured.

TABLE 2 % Change in Temp R. H. Time Leakage (° C.) (%) (hours) Cap DFESR Current Example 1 85 85 1000 10 −10 20 0 Example 2 85 85 1000 −10010000 15000 0

The capacitors of Example 1, which have a barrier layer, were much morestable after aging in such environments, and showed much less change inproperties

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

1. A solid electrolytic capacitor comprising: an anode; a dielectriclayer overlying the anode; a protective adhesive layer overlying thedielectric layer, wherein the protective adhesive layer comprises apolymer having a repeating unit with a functional hydroxyl group,wherein the polymer has a degree of hydrolysis of at least about 90 mole%; and a solid electrolyte layer overlying the protective adhesivelayer.
 2. A solid electrolytic capacitor as in claim 1, wherein thepolymer comprises a hydrophilic polymer.
 3. A solid electrolyticcapacitor as in claim 1, wherein the polymer has a degree of hydrolysisof at least about 95 mole %.
 4. A solid electrolytic capacitor as inclaim 1, wherein the polymer is poly(vinyl alcohol) or a copolymerthereof.
 5. A solid electrolytic capacitor as in claim 1, wherein theprotective adhesive layer further comprises an acrylate, methacrylate,or a combination thereof.
 6. A solid electrolytic capacitor as in claim1, wherein the protective adhesive layer has a resistivity of greaterthan about 5 ohm-cm.
 7. A solid electrolytic capacitor as in claim 1,wherein the protective adhesive layer has a resistivity of greater thanabout 1000 ohm-cm.
 8. A solid electrolytic capacitor as in claim 1,wherein the protective adhesive layer has a thickness of about 50micrometers or less.
 9. A solid electrolytic capacitor as in claim 1,wherein the solid electrolyte layer comprises a conductive polymer. 10.A solid electrolytic capacitor comprising: an anode; a dielectric layeroverlying the anode; a protective adhesive layer overlying thedielectric layer, wherein the protective adhesive layer comprises apolymer having a repeating unit with a functional hydroxyl group; and asolid electrolyte layer overlying the protective adhesive layer, whereinthe solid electrolyte layer comprises a conductive polymer, and whereinthe conductive polymer is polymerized in the presence of less than astoichiometric amount of the oxidative polymerization catalyst.
 11. Asolid electrolytic capacitor as in claim 1, further comprising a barrierlayer overlying the solid electrolyte layer.
 12. A solid electrolyticcapacitor as in claim 1, wherein the anode contains a valve metal.
 13. Asolid electrolytic capacitor as in claim 12, wherein the anode containstantalum or a niobium oxide.
 14. A solid electrolytic capacitor as inclaim 10, wherein the polymer has a degree of hydrolysis of at leastabout 90 mole %.
 15. A solid electrolytic capacitor as in claim 10,wherein the polymer has a degree of hydrolysis of at least about 95 mole%.
 16. A solid electrolytic capacitor as in claim 10, wherein thepolymer is poly(vinyl alcohol) or a copolymer thereof.
 17. A solidelectrolytic capacitor as in claim 10, wherein the protective adhesivelayer further comprises an acrylate, methacrylate, or a combinationthereof.
 18. A solid electrolytic capacitor as in claim 10, wherein theprotective adhesive layer has a resistivity of greater than about 5ohm-cm.
 19. A solid electrolytic capacitor as in claim 10, wherein theprotective adhesive layer has a resistivity of greater than about 1000ohm-cm.
 20. A solid electrolytic capacitor as in claim 10, wherein theprotective adhesive layer has a thickness of about 50 micrometers orless.
 21. A solid electrolytic capacitor as in claim 10, furthercomprising a barrier layer overlying the solid electrolyte layer.
 22. Asolid electrolytic capacitor as in claim 10, wherein the anode containsa valve metal.
 23. A solid electrolytic capacitor as in claim 22,wherein the anode contains tantalum or a niobium oxide.
 24. A solidelectrolytic capacitor comprising: an anode containing a valve metal; adielectric layer overlying the anode; a protective adhesive layeroverlying the dielectric layer, wherein the protective adhesive layercomprises a vinyl alcohol copolymer, wherein the vinyl alcohol copolymeris at least 90 mole % hydrolyzed; and a solid electrolyte layeroverlying the protective adhesive layer.
 25. A solid electrolyticcapacitor as in claim 24, wherein the vinyl alcohol co-polymer is formedfrom a monomer that includes an acrylic ester, methacrylic ester, or acombination thereof.
 26. A solid electrolytic capacitor as in claim 24,wherein the protective adhesive layer has a resistivity of greater thanabout 5 ohm-cm.
 27. A solid electrolytic capacitor as in claim 24,wherein the protective adhesive layer has a thickness of about 50micrometers or less.
 28. A solid electrolytic capacitor as in claim 24,wherein the solid electrolyte layer comprises a conductive polymer. 29.A solid electrolytic capacitor as in claim 24, wherein the anodecontains tantalum or a niobium oxide.
 30. A solid electrolytic capacitorcomprising: an anode; a dielectric layer overlying the anode; aprotective adhesive layer overlying the dielectric layer, wherein theprotective adhesive layer comprises a polymer having a repeating unitwith a functional hydroxyl group, wherein the polymer is a vinyl alcoholco-polymer formed from a monomer that includes an acrylic ester,methacrylic ester, or a combination thereof; and a solid electrolytelayer overlying the protective adhesive layer, wherein the solidelectrolyte layer comprises a conductive polymer.
 31. A solidelectrolytic capacitor as in claim 30, wherein the monomer comprisesmethyl methacrylate.
 32. A solid electrolytic capacitor as in claim 30,wherein the polymer has a degree of hydrolysis of at least about 90 mole%.
 33. A solid electrolytic capacitor as in claim 30, wherein thepolymer has a degree of hydrolysis of at least about 95 mole %.
 34. Asolid electrolytic capacitor as in claim 30, wherein the protectiveadhesive layer further comprises an acrylate, methacrylate, or acombination thereof.
 35. A solid electrolytic capacitor as in claim 30,wherein the protective adhesive layer has a resistivity of greater thanabout 5 ohm-cm.
 36. A solid electrolytic capacitor as in claim 30,wherein the protective adhesive layer has a resistivity of greater thanabout 1000 ohm-cm.
 37. A solid electrolytic capacitor as in claim 30,wherein the protective adhesive layer has a thickness of about 50micrometers or less.
 38. A solid electrolytic capacitor as in claim 30,wherein the solid electrolyte layer comprises a conductive polymer. 39.A solid electrolytic capacitor as in claim 30, wherein the conductivepolymer is polymerized in the presence of less than a stoichiometricamount of the oxidative polymerization catalyst.
 40. A solidelectrolytic capacitor as in claim 30, further comprising a barrierlayer overlying the solid electrolyte layer.
 41. A solid electrolyticcapacitor as in claim 30, wherein the anode contains a valve metal. 42.A solid electrolytic capacitor as in claim 41, wherein the anodecontains tantalum or a niobium oxide.